The separation of various substances through selective adsorption may be effected using a simulated moving bed of adsorbent, such as that described in U.S. Pat. No. 2,985,589. In accomplishing this simulation, it is necessary to connect streams entering and exiting a series of beds in a sequential pattern. These beds may be considered to be portions of a single large bed whose movement is simulated by the movement of the entry or exit points of each of the streams. Each time one stream destination is changed, the destinations or origins of other related streams, which may be streams entering the beds or leaving the beds, is changed simultaneously. The moving-bed simulation may be described simply as dividing the bed into a series of fixed beds and moving the points of introducing and withdrawing liquid streams past the series of fixed beds instead of moving the beds past the introduction and withdrawal points of such streams.
It is highly desirable to use a single device to simultaneously transfer all of the fluid streams, thereby avoiding the obvious problems associated with numerous separate valves which must be simultaneously actuated. The multiport rotary disc valve of U.S. Pat. No. 3,040,777 provides a valve design to effect a simulated moving bed. This valve effects simultaneous interconnection of conduits which provide the streams entering and leaving the simulated-moving-bed adsorption system with the conduits associated with the individual beds which supply and remove streams to and from the beds in which one conduit is connected between each two beds. It is to be noted that each conduit of the second group serves that dual function of supply and removal, so that it is unnecessary to provide conduits for supplying streams separate from those for removing streams.
There are variations in process requirements in different moving bed simulation processes, resulting in different flow schemes and thus variations in rotary valve arrangement. For example, in addition to the four basic streams described in U.S. Pat. No. 2,985,589, it may be desirable to utilize one or more streams to purge, or flush, a conduit to prevent undesirable mixing of components. U.S. Pat. No. 3,201,491 provides information on flushing lines as applied to the simulated-moving-bed process. Passing fluid through a bed or beds in the reverse direction from normal flow, commonly known as backflushing, is treated in U.S. Pat. No. 4,319,929. Relevant portions of all of the foregoing patents are incorporated herein by reference thereto.
U.S. Pat. No. 4,574,840 discloses a multiport axial valve having a rotor assembly inside a stator assembly. The stator assembly comprises a central element and two end elements, each of which has a cylindrical form, with the central element having transverse surfaces perpendicular to the longitudinal axis of rotation. The rotor assembly comprises a spacer element between two end elements, effecting annular volumes between rotor and stator end elements and transverse volumes between the stator central element and rotor end elements, configured such that axial forces exerted by fluid streams balance the rotor assembly. However, this reference does not suggest the seating surfaces or port configurations of the present invention.
U.S. Pat. No. 6,802,970 B2 teaches a distributing device comprising a revolving disc mounted in a stationary housing in sealing engagement. Feed pipes and discharge pipes open into passageways via at least one ring-shaped duct in a closed circle around the axis of rotation. This reference differs from the present invention in the configuration of the rotor, and does not suggest the port configuration central to the present invention.
U.S. Pat. No. 6,904,936 discloses a rotary valve having a stator of barrel shape with first ports spaced longitudinally along the lateral structure and second ports at the bottom around the axis of the stator and a rotor having a hollow shaft section with longitudinally spaced top openings, a plurality of flow passages, and bottom openings spaced consistently with those of the stator; a plurality of ring structures between the stator and rotor forming a circular groove between two adjacent ring structures for fluid communication in a sequential and cyclic manner. The arrangement of ports differs from that described herein and does not suggest the configuration of the present invention.
With the widespread commercial acceptance of simulated-moving-bed processes using multiport rotary disc valves as described in the known art, single process units currently are being designed and/or contemplated with capacities which require two or more rotary valves. A valve design according to the present invention in which a single unit is effective at increased capacities provides significant economies of scale.